Portable fire extinguishers based on two-phase flow, consisting of a vessel containing a liquid phase interconnected to a source of pressurized gaseous phase and a head assembly with a shut-off valve and a discharge nozzle, are well known. Upon infusing gaseous phase into the liquid phase and releasing the shut-off valve, both phases begin to flow through the unit's head or some other intermediate element to the discharge nozzle. The gaseous phase is usually carbon dioxide, nitrogen or compressed air. Water or other liquids having fire-extinguishing capabilities, at times with the addition of a foaming agent, are used as the liquid phase. A vessel containing pressurized gaseous phase, located either inside or outside the vessel holding liquid phase, constitutes the source of the gaseous phase. The gaseous phase is introduced via a gas tube immersed in the liquid phase vessel near the inlet of the flow tube. Following an increase of pressure inside the vessel containing the liquid phase both phases are forced through the flow tube to the nozzle assembly, wherein mixing of the two phases takes place during the continuous flow of the gaseous phase. The disadvantage of these solutions is that the relative amount of phase mixture content is variable and the pressure and flow rate fall rapidly during the discharge cycle, and this causes flow perturbations and gradual deterioration of fire extinguisher performance.
Well known too are liquid atomizers equipped with a vessel containing a liquid phase interlinked via a gas valve to a gaseous phase vessel, where the gaseous and the liquid phases are delivered to a mixing chamber via separate conduits, and the mixing chamber is next connected to a spray nozzle via a singular flow tube.
Patent publication EP 1197245 depicts a portable foam extinguisher equipped with a pistol-shaped nozzle assembly connected via a mixing chamber to a tank holding liquid phase and a source of gaseous phase. Upon opening the gas valve, liquid phase is forced into the mixing chamber wherein a stream of liquid collides with a stream of gas arriving via a gas tube from the gaseous phase source. Next both phases are transported via a flow conduit executed in the unit's head to the spray nozzle. Additional accessories are used to adjust the relative proportion of gaseous and liquid phases delivered to the mixing chamber. This design allows the generation of a two-phase flow in the mixing chamber and the transfer of the two-phase mixture under pressure to the spray nozzle, where the fire-suppression agent undergoes expansion. This extinguishing device is designed to operate under a working pressure in the range from 25 to 35 bar.
Patent application WO 9524274 presents a device to extinguish fires wherein a two-phase flow is generated in a mixing chamber. Upon introduction of both phases into the chamber, a plug flow wherein portions of the gaseous and liquid phases remain separate, is generated in a conduit connecting the mixing chamber with the nozzle. This device allows for the generation of a dispersed stream of liquid at the nozzle exit with the streamed discharge featuring pulsation-like characteristics. In the technical field of patent application WO9524274, devices to generate two-phase flows with a prescribed relative proportion of gaseous phase in the liquid phase are presented, within which a system of metering valves or manipulators open and close on an interchanging basis the supply conduits of phases into the mixing chamber. This requires fast transport of the gaseous phase intermixed in the liquid phase. Use of such phase interchangers based upon pulsating flows is limited to fixed systems working at a pressure which is constant and for which the pressure differential between the phases remain limited, or to those having an external source of power driving the manipulator.